Why Was The Collapse Of Political Institutions More Devastating To The Roman Empire Than The Han

Lets say that the Roman Empire somehow avoided collapse and survived to this day, what would it look like?

This is the last of the Roman Empire:On 8 October 1912, during the First Balkan War, Lemnos became part of Greece. The Greek navy under Rear Admiral Pavlos Kountouriotis took it over without any casualties from the occupying Turkish Ottoman garrison, who were returned to Anatolia. Peter Charanis, born on the island in 1908 and later a professor of Byzantine history at Rutgers University recounts when the island was occupied and Greek soldiers were sent to the villages and stationed themselves in the public squares. Some of the children ran to see what Greek soldiers looked like. ‘‘What are you looking at?’’ one of them asked. ‘‘At Hellenes,’’ the children replied. ‘‘Are you not Hellenes yourselves?’’ a soldier retorted. ‘‘No, we are Romans." Thus was the most ancient national identity in all of history, preserved in isolation, finally absorbed and ended.Kaldellis, Anthony (2008). Hellenism in Byzantium: The Transformations of Greek Identity and the Reception of the Classical Tradition. Cambridge, UK: Cambridge University Press. ISBN 0521876885. pages 42-43What the heck, you ask?The Roman Empire was split into the Western and Eastern Roman Empires. The Western one was completely destroyed, while the Eastern one survived into the Middle Ages as a unified polity, now called the Byzantine Empire or Byzantium. The Ottoman Empire destroyed and took over the lands that had belonged to the Eastern Roman Empire, including Lemnos. But the people didn’t get the memo.The legacy of the Roman Empire was also continued into the Middle Ages and beyond via the Holy Roman Empire (the proto-German and sometimes including Italian confederacy that was not holy, not Roman, and not an empire) and the Russian Empire, whose rulers styled themselves as Caesars… localized as Kaiser (German) and Czar or Tsar (Russian). Even though these “Romans” were dethroned due to World War I, the legacy subtly lives on:

Why did the Roman Empire fall?

A slave based society can not pass through the next stage of economic development which is industrialization. No need to make a work saving device, just get more slaves. - ( I put this before barbarian invasion because if the Roman empire was able to grow economically it could make up for so many failures on the battlefield. )A slave based society amplifies the difference between the haves and have nots. Not just between slaves and freemen, but between rich slave holders and poor unemployed freemen. This greatly reduced the amount of stake holders within the Empire. Why should you fight to defend a society you have no stake in?The Emperor system neither produced good Emperors on a regular basis or allowed for a peaceful line of succession. Civil War is the most wasteful and dangerous of enterprises when faced with an outside enemy.The Emperor system also needlessly added to the states bureaucracy. Just one example is Governor-ships. With each new Emperor political favors need to be payed back and new Govern-ships where created until the ranks of Governors swelled beyond what would of been recognizable in the 1st century.In the 3rd century AD, for reasons not completely understood today central Asian horsemen poured out to of the Russian steppe pushing Germanic tribes in front of them, pressing them up against the Empire.Extended conflict along the Rhine/Danube, and the extensive use of Germanic mercenaries allowed a technology transfer to such a degree that by the 4th century it was difficult to tell the difference from a German in the Roman army and one that was fighting the Roman army.The reopening of the Silk Route allowed the freer movement of goods and ideas, but also plague. Plague ravaged the Empire who’s densely populated cities where highly vulnerable.These pressures and mismanagement pushed the Roman tax system beyond the Laffer curve optimum. Taxes where pushed higher, revenues fell and then taxes where pushed higher again. The currency depreciated and the amount of silver used in the coinage was reduced by dilution.

What happened to the rest of the Romans after the Roman Empire fell, and why didn't anyone gather the rest of the Romans and try to rebuild?

The short answer is they did what they could, but the situation was not recoverable.  Rome wasn't swamped in invading barbarians (see What were the sackings of Rome in the year 410 by the Goths and Vandals like? Were they organized or did they just ride through the city slashing, burning and pillaging?)  As the other answers note, the eastern half of the empire survived and tried to reconquer the west under Justinian (see Why was the Eastern Roman Empire never able to take back the territory to its west after the Western Roman Empire fell? for more details).  Parts of Italy and Sicily remained under Byzantine control until the 11th century. The real problem was the loss of the richest parts of the eastern Empire to the Arabs in the 600's.  This put the Byzantines on the permanent strategic defensive: not only did they have to worry about their own survival, the old Mediterranean world on which the Roman empire thrived was forever split into mutually hostile camps.  In the heyday of the empire it was easier and cheaper to get from Rome to Alexandria, Antioch or Jerusalem than to go to Lutetia (Paris) or Vindobona (Vienna); the whole economic and political structure of antiquity was based on the sea.  Once the southern shore of the Mediterranean was in the hands of an arch-enemy the "Roman" world could never be put back together.On the other hand, the dream of unity died hard. Charlemagne, re-united much of the western empire and assumed the title of Roman emperor in 800.  He may look to us like a "Medieval" king but he was very self-conscious about being the heir of the Caesars:Karolus Imperator Augustus:  Charlemagne = Caesar.Charlemagne's empire did not include the old Roman provinces of Spain but it did include almost all of Gaul, Italy north of Rome, and the old frontier provinces of Rhaetia and Noricum.  It carried on its business in Latin, it busied itself with the preservation of classical literature.  Charlemagne himself was a Frank -- but Rome had non-Roman emperors as early as Trajan in the year 98.   It was a ramshackle business compared to the heyday of Rome (though, by the end of his reign Gaul in particular had recovered its population to levels not seen in 400 years)  but it was a powerful testament to the long shadow cast by the idea of a united "Roman" world.Charlemagne's "Holy Roman Empire" lasted, in attenuated form, until 1806.